ABSTRACT A major goal of my career is to become an independent scientist studying the mechanisms of rare genetic disorders, with the ultimate goal of developing therapies. Charcot-Marie-Tooth (CMT) disease is a debilitating inherited peripheral neuropathy that affects 1 in 2,500 individuals worldwide. However, a rare, autosomal dominant form of CMT is caused by mutations in five genes encoding an aminoacyl-tRNA synthetase (ARS). Aminoacyl-tRNA synthetases ligate tRNA molecules to cognate amino acids for use in protein translation. Although the majority of CMT-associated mutations impair this catalytic activity, the precise molecular pathology is not understood. Interestingly, neuropathy-associated ARS mutations are all missense changes; frameshift and nonsense mutations in ARS genes are not associated with CMT disease and are present in unaffected individuals, ruling out haploinsufficiency. Additionally, the five ARS genes implicated in CMT encode homodimeric enzymes. These observations raise the possibility of a dominant-negative effect that causes a severe depletion of ARS activity, which may breach a minimum threshold of enzyme function required for healthy peripheral nerves. Under a dominant-negative mechanism: (i) neuropathy-associated ARS missense variants should directly impact protein translation and the wild-type enzyme should rescue the neuropathic phenotype; and (ii) loss-of-function missense variants in any dimeric ARS enzyme should be potentially deleterious to peripheral nerves. To determine if ARS-associated neuropathy arises due to reduced ARS activity, we will: (1) study an established CMT-causing ARS mutation to define the molecular pathology; and (2) engineer loss-of-function mutations in a dimeric ARS enzyme not-yet-associated with CMT disease and test for neurotoxicity in vivo. These experiments will strengthen our understanding of the mechanism of ARS- mediated CMT disease, and will directly test if improving ARS function is a relevant therapeutic goal for patient populations. Importantly, this project will allow me to develop the skill set necessary for a research career focused on defining the molecular mechanisms of rare, inherited human diseases.